or Internet service companies, the aftermath of last week's terrorist attacks has meant new scrutiny of the material that their online users can view and post.

Whether it is Web sites supporting terrorism, or backlash anti-Islamic messages posted on Internet bulletin boards, some material has forced the Internet access providers to step up their screening efforts or rethink their standards of what sort of material is acceptable.

On one Web site, under the heading "The Road to Jihad," an urban skyline was shown in flames and its reflection mirrored on the water of a harbor. In the computer-graphics image of flames were burning flags of the United States and Israel.

Another of these Web sites had animations of dripping blood, Kalashnikov automatic weapons and admonitions to vanquish the "enemies of Allah" by any means necessary. The message board of another site offered practical advice for handling guns: "Also try loading your weapons with gloves on so as not to leave any fingerprints. Disposable latex gloves do nicely."

Still another site had audio and video clips of speeches by Osama bin Laden, the Saudi exile widely thought to be behind the World Trade Center and Pentagon attacks, as part of his proclaimed jihad, or holy war, against the United States and its allies. The Web site encouraged supporters to send money to a bank in Pakistan, providing account numbers. And it urged believers to join the movement and apply their skills in "training camps, refugee camps and battlefronts."

But by the end of the week, far fewer such sites were still up on the Web. Many that had used the Web host, directory and message services of American Internet companies had been pulled down, either by the companies or voluntarily.

Other such sites came under attack from enraged Web surfers. One of the jihad sites had been covered with a picture of Mr. bin Laden under the headline, "Wanted For Murder."

The grass-roots backlash sometimes turned ugly, and later in the week the administrators of some Internet services were largely focused on eliminating inflammatory anti- Islamic postings. One of the messages on an Islamic group section of America Online stated, "Kill all of those who worship Allah."

"Men, women and children," it said, adding, "and do it slowly and totally."

The practical issue for Internet service companies is far more one of "community standards" than of law. The objectionable images, the advocacy of violence and the venomous pronouncements ・both on some of the jihad sites and in the anti-Islamic backlash ・are generally shielded under free-speech protections.

A legal landmark was a Supreme Court ruling in 1969, Brandenburg v. Ohio, which dealt with a Ku Klux Klan leader who had graphically advocated violence against blacks and Jews at a Klan rally filmed by local television crews. The Supreme Court found that such comments, however obnoxious, were protected as free speech unless the advocacy of violence represents a "clear and present danger" and prosecutors can show that it is intended to "produce imminent lawless action."

But the community standards that most Internet service providers apply can be more restrictive. Most of the companies have "terms of service" guidelines that typically prohibit postings or images the administrators deem racist, hateful or advocating violence. The guidelines often ban the display of material that is determined to be offensive, according to quite subjective standards like "harmful," "threatening," "harassing" or "invasive of another's privacy."

Online community standards have evolved and been redefined in response to public and subscriber criticism. With online pornography, leading Internet services ・America Online, Yahoo (news/quote) and others ・have steadily moved to restrict not only content they deem pornographic, but also to curb the ability of people to find pornographic sites through links, directory and search features.

A similarly heightened sensitivity to other subjects may develop in the wake of the terrorist attacks last week. John C. Dvorak, a columnist for PC magazine, said: "I find the inflammatory material on some of these jihad sites much more deplorable than pornography. The Internet services should re-evaluate their policies and enforcement after what happened on Tuesday."

There is every indication that the companies are doing just that, both with the jihad sites and the anti- Islamic postings.

AOL added screeners, and the screening team was told "to be particularly vigilant about hate speech," a company spokesman, Andrew Weinstein, said. Violators were warned that they could be expelled from the service.

Like some other major Internet companies, Terra Lycos (news/quote) has a hosting service that enables people to put up Web sites. One of the jihad sites was on its Tripod Web-hosting service, and Geoff Strawbridge, director of customer service for Terra Lycos, said to a reporter, "You brought this site to our attention, and our policy prohibits anything that is hateful or harmful." The site was taken down.

A message site on Boardhost.com for "mujahideen," or holy warriors, had a posting that gave weapons- handling tips. It was followed by a message urging the weapons expert to "die" in graphic terms.

After these postings were pointed out to Jeremy Gallagher, founder and president of Boardhost.com, the message board was one of a handful that he removed last week.

Yahoo's Geocities service provides hosting services for members, including a few jihad sites, and the Yahoo directory and search features have links to many of them. Asked on Wednesday to look at a few, Nicki Dugan, a Yahoo spokeswoman, said that at a glance "some of these are probably clearly a violation of our terms of service, and others are probably part of a debate about what's Islamic fundamentalism."

By the end of the week, several of the sites were down.

Large Internet access providers typically have monitoring teams, but with millions of users they are mainly policed by their members. They rely on users to bring perceived abuses to the attention of the service administrators, and their community standards are shaped by the collective will of users.

As Mr. Strawbridge of Terra Lycos said: "We do recognize that the world did change this week. I'm sure it's going to change community standards and practices, but it is hard to say just how."